In the laying of asphalt pavement roadways, for example, it is common to utilize floating screed type pavers. In pavers of this type, a paver tractor is advanced along the roadbed, typically pushing ahead of it a truck containing a supply of hot asphalt. The hot asphalt material is conveyed to the back of the paver, by internal conveyor means, and deposited in front of the floating screed. The paving material is distributed in front of the screed, and then leveled and smoothed by the advancing screed, as it travels over the just deposited asphalt material.
Inasmuch as the internal conveyor means of the paver is typically narrower in width than the screed, conventional floating screed pavers are provided with transversely disposed rotating auger-like distribution means, positioned directly in front of the screed. The auger-like means serve to move the deposited asphalt material laterally, and to distribute it with some degree of uniformity in front of the advancing screed. Ideally, the transverse width of the auger-like means is approximately the same as the width of the screed, in order to assure distribution of the paving material to the extremities of the screed.
In order to accommodate laying of pavement mats of different width, the design of conventional paving machines typically has provided for the use of extension attachments for both the screed and auger facilities. Thus, for over-the-road travel, either self-powered or by truck, the paver is configured for minimum width. At the job site, extension attachments are mounted to the screed and to the auger-like distributor, to increase the paving width of the machine to meet the demands of the job.
It has been known heretofore to construct a floating screed paver with a power extendable/retractable screed arrangement, enabling the operator of the paver to vary the effective width of the screed at any time, even while the paver is in motion and in operation. Originally, such power variable screed arrangements were utilized primarily in connection with special paving jobs, such as driveways, parking lots, etc. where considerable width variability might be expected. Increasingly, however, paving contractors are preferring power variable screed constructions even for extended highway paving, where there may be minimum variability in the width of the paving mat. Such power variable screed facilities provide the contractor with a great degree of flexibility, and also can result in considerable savings of set-up and knock-down time at the beginning and end of paving operations. An advantageous form of such power variable screed for an asphalt paver is described in the Robert L. Brown, U.S. Pat. No. 4,379,653, assigned to White Consolidated Industries, Inc., the disclosure of which is incorporated herein by reference.
One of the shortcomings of asphalt paving equipment utilizing any of the existing power variable screed arrangements is that the auger-like mechanisms, utilized for distributing the paving material across the full width of the screed, do not vary along with the adjustments in screed width. This can cause problems in the uniformity of the pavement mat, particularly near the outer extremities of an extended screed. One attempt to overcome problems of this type is reflected in the Fisher et al. U.S. Pat. No. 3,907,451, in which auger devices are mounted directly on a movable strike-off element such that, when the strike-off element is moved in a laterally outward direction, it carries the auger mechanism with it. This does little to solve the material distribution problem, however, because moving the augers in an outward direction leaves an area in the center, where the bulk of the material is being deposited, without means to move it laterally outward. Further, the mounting of an auger on a screed or strike-off element serves to impose widely varying reaction forces on the screed or strike-off element, which can have the effect of introducing undesirable variations in the finish of the pavement mat.
Pursuant to the present invention, a novel and improved material distribution arrangement is provided for an asphalt paving machine, particularly a machine equipped with a power variable floating screed, in which an auger-like distribution mechanism is of telescoping construction capable of expanding laterally, either along with or independently of the power extendable screed. The new arrangement represents a vast improvement in existing asphalt pavers with power variable screeds, in that under all conditions it is assured that there will be an effective distribution of the paving material laterally in front of the extended screed.
To advantage, the power extendable material distribution mechanism of the invention is mounted and supported on the paver tractor, independently of the floating screed, so that the action of the screed is not affectd by the variable reaction forces typically acting upon the distribution mechanism.
In a highly advantageous form, the power extendable distributor arrangement of the invention is comprised of telescopically associated auger-like sections, each containing a plurality of paddle-like deflector plate segments arranged to an angle to the rotational axis of the auger mechanism. When the mechanism is in its fully condensed or retracted position, the various deflector segments optimally may be aligned to form a more or less continuous helix, although that is not necessary to the invention. When extended or partially extended, the deflector segments are distributed over the full length of the device and act with a high degree of effectiveness on the deposited paving material to provide a desired degree of uniformity in the distribution thereof out to the farthest reaches of the extended screed.
Among other features of the invention, the power variable auger-like distributor mechanism of the invention is designed to be suitable for operation in the extremely hostile environment, such as that represented by hot asphalt material, in which the distributor mechanism is immersed or partially immersed during normal operations. Initially, the asphalt material is hot and plastic, but it accumulates and hardens over time, such that any mechanism operating in its environment must be rugged and dependable in construction, and have a measure of self-cleaning action to minimize the likelihood of the mechanism being "frozen" by congealed asphalt.
As a subsidiary feature, the apparatus of the invention incorporates an advantageous form of telescoping material confinement panel structure, positioned in front of the telescoping distributor mechanism and extendable or retractable along with it. The confinement panel works in cooperation with the screed to confine the deposited paving material, but in front of and behind the distributor mechanism, over its adjustably extended length. In addition, the panel structure serves as an extendable guard, so that workmen are fully protected from accidental contact with the rotating distributor plates.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments and to the accompanying drawing.